Power over Ethernet (PoE), which is outlined in IEEE Std 802.3™-2005 clause 33 (the PoE standard), refers to a technique for delivering power and data to an electronic device via Ethernet cabling. In a PoE system, a power sourcing equipment (PSE) device provides a power supply to electronic devices, which may be referred to as powered devices, via an Ethernet cable. PoE eliminates the need for a separate power source to deliver power to attached powered devices. Such powered devices may include voice over Internet protocol (VoIP) telephones, wireless routers, security devices, field devices to monitor process control parameters, data processors, other electronic devices, or any combination thereof.
In general, the PoE standard requires each of the Ethernet ports associated with a powered device (i.e., an electronic device that receives both power and data from the Ethernet cable) to be adapted to suppress transient power surges in excess of 1000 mA for short durations. Such transient power events may be induced via electrostatic discharges to the Ethernet cabling, for example, during attachment and detachment of Ethernet enabled devices. Conventionally, such surge suppression includes an external zener diode having a breakdown voltage of approximately 64 volts, which, in response to receiving an input voltage in excess of 64 volts, breaks down to conduct current power between a positive supply terminal and a negative supply terminal. Typically, an external zener diode is used instead of an integrated zener diode to dissipate heat, so that when the zener diode breaks down and conducts current, the heat dissipated by the zener diode does not damage other circuitry. However, such external zener diodes are expensive relative to integrated zener diodes.